The proposed project will be a five-year continuation of a four- year grant designed to investigate parent, sibling, and peer influence on adolescent use of cigarettes, alcohol, marijuana, and smokeless tobacco. A sample of 763 families was initially recruited who are currently completing their third annual assessment. Measures included questionnaires completed by all members of the family over the age of 11 and living at home. More intensive investigations were conducted with a subset of the families who participated in individual interviews and parent- adolescent problem-solving interactions. The proposed research is designed to extend this longitudinal data set to late adolescence and young adulthood with the following aims. (a) To chart the developmental process of substance use in these age groups; (b) to identify familial, personal, and peer risk and protective factors that predictive of the onset and maintenance of substance use in adolescence and adulthood, (c) to examine the consequences of substance use and its reciprocal effects on socio-cognitive and behavioral factors, (d) within a mutiple-cohort design, to follow five cohorts over an eight-year period to separate historical from development effects, and (e) to contrast different theoretical models of the acquisition and progression of drug use.